Bacterial peptidoglycan is a cross-linked polymer of NAG-NAM (N-acetyl-glucosamine + N-acetyl-muramic acid) with pentapeptide cross-links forged by transpeptidase enzymes (penicillin-binding proteins, PBPs). β-lactams (penicillins, cephalosporins, carbapenems, monobactams) mimic the D-Ala-D-Ala terminus of the pentapeptide → acylate the PBP active-site serine → halt cross-linking → osmotic lysis (bactericidal in growing bacteria). β-lactamases hydrolyze the β-lactam ring; β-lactamase inhibitors (clavulanate, tazobactam, sulbactam, avibactam, vaborbactam) preserve the partner antibiotic. Vancomycin works upstream — binds the D-Ala-D-Ala terminus directly, preventing transpeptidation; resistance via D-Ala-D-Lac (VRE) or thickened cell wall (VISA).
Organ Systems
immune-hematologic
Pathway Steps
d-ala-d-ala-terminus → peptidoglycan-crosslink — via PBP transpeptidase forms the cross-link → mature peptidoglycan. Bacterial cell-wall strength comes from peptidoglycan cross-links formed by transpeptidases (penicillin-binding proteins) acting on the D-Ala-D-Ala terminus. β-lactams mimic this terminus to irreversibly inhibit the transpeptidases, while vancomycin binds the D-Ala-D-Ala directly — two classes attacking the same essential cross-linking step.
Known Modulators
penicillin v (inhibitor) — PBP (β-lactam). narrow-spectrum natural penicillin; strep + Treponema; PO well-absorbed; 4-6h t½
ampicillin (inhibitor) — PBP (β-lactam). aminopenicillin; broader gram-negative vs penicillin-V; Listeria coverage in meningitis combo
amoxicillin (inhibitor) — PBP (β-lactam). aminopenicillin; better PO F than ampicillin (~95% vs ~50%); first-line otitis media + H. pylori triple therapy
amoxicillin clavulanate (inhibitor) — PBP + β-lactamase inhibitor (clavulanate). Augmentin; clavulanate suicide-inhibits class-A β-lactamases → extends amoxicillin coverage to amoxicillin-resistant H. influenzae + M. catarrhalis